Reservoir multiphase transport properties such as relative permeability and capillary pressure are important parameters for reservoir characterization, management, forecasting and performance analysis. It is known to use wireline logging tools to measure native formation resistivity in order to help estimate multiphase flow parameters. For example, co-owned U.S. Pat. No. 5,335,542 describes characterization of formation properties by combining probe pressure measurements with resistivity measurements from electrodes mounted on a pad in wireline formation tester. As fluid is withdrawn or injected into the formation at known rates, the fluid pressure of the formation and electromagnetic data are obtained. The electromagnetic and fluid pressure data can then be processed using various formation and tool models to obtain relative permeability information, endpoint permeability and wettability.
Drilling mud is usually weighted to maintain wellbore hydrostatic pressure above that of the formation in order to prevent the well from blowing out. This causes borehole fluids to enter the formation. Further, as the borehole fluids enter the formation, a mudcake is deposited on the borehole surface. The presence of a fluid-invaded region and mudcake around the borehole distorts the logs and can therefore make interpretation difficult. Conversely, the displacement of one fluid by another leads to a characteristic signature that may be used to infer multiphase flow properties, provided the underlying physics is taken into account, such as described in U.S. Pat. No. 5,497,321.
One problem with calculating multiphase transport properties based on measured resistivity is that aspects of intentional fluid introduction and resistivity measurement are difficult to control. For example, it is difficult to create timely and uniform changes in salinity within the borehole from which distinct fronts of contrasting salinity would be created. Also, electrical pathways within the borehole and along the borehole wall can affect formation resistivity measurement. This is described in U.S. Pat. No. 6,061,634.